P-044: RETROSPECTIVE STUDY OF POST-TRANSFUSION ALLOIMMUNIZATION IN THE SICKLE CELL POPULATION OF THE CHR CITADELLE
Authors: SEPULCHRE E., MINON J., PARIDAENS H., STOJKOVIC V., KETELSLEGERS O., DRESSE M.
Journal: HemaSphere (2022)

Purpose: Red blood cells transfusion is a mainstay in the management of sickle cell disease (SCD). However, this medical procedure is not without risk, particularly in patients with SCD. Indeed, they are particularly at risk of post-transfusion alloimmunization for several reasons. This complication will lead to an increased risk of additional immunizations, delayed hemolytic reactions and reduced chances of finding compatible blood products. The objective of this work is to evaluate, through a retrospective study, the effectiveness of the transfusion policy adopted at the regional hospital center of the Citadelle in Liège (Belgium). Materials and methods: We studied clinical and immunohematological data in SCD population. Our cohort consisted of 164 patients followed regularly at the hospital’s SCD center. The different sickle cell syndromes were represented (SS, SC, S/β0, S/β+). Results: Seventy-four percent of our cohort was transfused (n=121), 91% (n=110) via our hospital blood bank. Our results reveal a post-transfusion alloimmunization rate of 19%. Antibodies directed against the RH system are predominant, with a rate of 38% (n=17), followed by the MNS system with a rate of 29% (n=13), the Lewis system with a rate of 18% (n=8), the Kell system with a rate of 7% (n=3), and finally the Duffy and Kidd systems, each with a rate of 4% (n=2) (Figure 1). Our study shows that advanced age, single transfusion, presence of an alloantibody, inflammatory background and an acute event are all risk factors for alloimmunization. We could not find any significant difference concerning gender, the presence of an autoantibody or splenectomy. RH genotyping has been performed in 87 patients. The distribution of the different RHD gene types found is shown in Figure 2. Phenotype has been changed from D-positive to partial D on the basis of this analysis for 35% of the patients, i.e. to be considered as D-negative for transfusion purposes. Among these patients, 2 had developed an anti-RHD antibody before the genotyping was performed. In 2017, prophylactic RH genotyping was implemented for all SCD patients. No anti-D was found since then. Conclusion: The significantly higher alloimmunization rate found in our SCD population is similar to rates reported in other centers meeting the guidelines. The major explanation probably lies in the difference in the distribution of erythrocyte antigens between African and Caucasian populations. The risk is particularly elevated for Rh system. That is why, in addition to the extended blood group phenotyping, prophylactic RH genotyping was introduced in our lab for all SCD patients since 2017. We have not detected any alloimmunization against antigens of this system since then. Alloimmunization risk factors highlighted in our study are consistent with the literature. In conclusion, the precautionary measures used in our center appear to be effective in minimizing the risk of post-transfusion alloimmunization in patients with SCD. However, improvement in this field still possible, including optimization of donor-recipient matches, better control of chronic inflammation associated with the disease and better understanding of genetic polymorphisms influencing the immune response.Figure 1. Distribution of specific alloantibodies according to erythrocyte antigenic systems.Figure 2. Distribution of RHD genes identified by genotyping. The authors do not declare any conflict of interest